Transgender (`trans') women (i.e., individuals with a feminine and/or female gender identity who were assigned male at birth) are among the populations at highest risk for HIV in the United States and worldwide. One of the most consistently reported contexts for HIV transmission among trans women is within a primary partnership with a non-transgender male. Despite the critical importance of primary partnerships for HIV prevention, the vast majority of HIV prevention studies and interventions for trans women have been individually-focused. For the past 10 years we have conducted research to identify intervention targets for reducing HIV transmission among trans women and their male partners using qualitative, survey, and intervention adaptation methodologies (R01DA018621; R34MH093232). Based on our conceptual and empirical understandings of HIV transmission risks among these couples, we recently developed and pilot tested the first known couples- based HIV prevention intervention for trans women and their male primary partner dyads (called ?Couples HIV Intervention Program?; CHIP), which was feasible, acceptable, and produced significant reductions in sexual risk behavior compared to the control group. Based on our highly successful R34 findings, we propose to test the efficacy of the CHIP program in large-scale randomized controlled trial (RCT) to reduce HIV risk among seroconcordant negative and serodiscordant couples. We will enroll racially diverse trans women and their male partners and randomize couples to either the CHIP intervention or an enhanced standard of care (SOC) control condition. Couples will be followed quarterly over 12-months. Analysis of study outcomes will utilize both individual- and dyadic-level data. Our primary outcome is a composite measure of risk for HIV transmission which encompasses validated behavioral indicators of HIV risk as well as biomedical confirmation of viral suppression and PrEP adherence. The CHIP intervention builds on years of formative work that targets interpersonal and social factors as mechanisms of HIV risk behavior among trans women and their male partners. If the CHIP intervention demonstrates efficacy in comparison to an enhanced SOC control condition, there will be support for implementing this approach within HIV prevention and care settings in order to reduce disparities in HIV transmission and acquisition among some of the highest priority HIV prevention populations.